Capacitive Sensing Circuit for Isolated Self and Mutual Measurement
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Solution Overview
Problem
Capacitive touch sensors face challenges in accurately measuring self and mutual capacitance, which affects their operation and can lead to decreased measurement accuracy due to sensitivity issues and nonlinear exponential voltage changes.
Innovation Solution
The development of a capacitive sensing circuit that allows for separate measurement of mutual and self capacitance using a switching capacitor technique, with specific circuit configurations and switching sequences to minimize the influence of self-capacitance on mutual capacitance measurement, and vice versa, ensuring accurate and linear current conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional capacitive sensing circuit is used to measure capacitance, then the circuit can detect touch input, but the measurement accuracy decreases due to sensitivity issues and nonlinear exponential voltage changes
Solution Approach 1:
The patent divides the capacitance measurement into two separate independent measurements: self-capacitance measurement and mutual capacitance measurement. This segmentation allows each measurement to be optimized independently, eliminating the interference and sensitivity issues that occur when trying to measure both simultaneously in conventional circuits.
Solution Approach 2:
The patent changes the measurement parameters by using separate measurement sequences with different switching configurations. The self-capacitance measurement uses one set of switching states while the mutual capacitance measurement uses a different set, allowing linear current conversion and accurate measurement without the nonlinear exponential voltage changes that plague conventional single-circuit approaches.
2Device complexity
If self-capacitance measurement is performed in the same circuit as mutual capacitance measurement, then the circuit structure remains simple, but the mutual capacitance measurement accuracy decreases due to self-capacitance influence
Solution Approach 1:
The patent implements periodic switching between different measurement modes. The circuit alternates between self-capacitance measurement phases and mutual capacitance measurement phases using non-overlapping clock signals. This periodic action allows the same physical circuit to perform both measurements sequentially with high accuracy, eliminating self-capacitance interference during mutual capacitance measurement while maintaining circuit simplicity.
Solution Approach 2:
The patent introduces switching capacitors and control switches as intermediary elements that isolate the self-capacitance and mutual capacitance measurement paths. These intermediaries allow the circuit to selectively connect different capacitor networks to the measurement node at different times, preventing self-capacitance from influencing mutual capacitance measurements while using the same basic circuit structure.
3Ease of manufacture
If conventional capacitance measurement methods are used, then the implementation is straightforward, but the measurement accuracy decreases due to sensitivity issues and nonlinear voltage changes
Solution Approach 1:
The patent replaces conventional direct voltage measurement methods with a charge integration approach using switching capacitors. Instead of measuring voltage directly (which suffers from nonlinear exponential changes), the circuit integrates charge over time using controlled switching sequences, producing a linear current conversion that is both easier to manufacture and more accurate.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables precise measurement of capacitance values, improving the accuracy and reliability of capacitive touch sensors, particularly in multi-touch detection systems by isolating self and mutual capacitance influences, thereby enhancing the performance of capacitive touch screens and other touch detection systems.
Implementation Method 1
a first current is proportional to a first capacitance value of the first electrode... a second current is proportional to a second capacitance value of the second electrode
Implementation Method 2
measuring the mutual capacitance between a first electrode and a second electrode of the capacitive touch sensor
Implementation Method 3
measuring the self-capacitance of the first electrode and the self-capacitance of the second electrode
Data Source
AI summary
In an example embodiment, an apparatus includes a sensing device. The sensing device includes circuitry configured to sense self-capacitance and circuitry configured to sense mutual-capacitance, each configured to detect capacitance values corresponding to whether an object is proximate to a touch screen. The sensing device is configured to measure a first capacitance value using the self-capacitance circuitry during self-capacitance sensing operations and to measure a second capacitance value using the mutual-capacitance circuitry during mutual-capacitance sensing operations.